The present invention relates to an automatic transmission
In recent years, automatic transmissions with multiple speed shifts have been demanded in order to improve fuel consumption, for example. Such an automatic transmission has been proposed that comprises (1) a speed reduction planetary gear that can output reduced speed rotation, wherein input rotation that is input to an input shaft has a reduced speed, and (2) a planetary gear unit that has multiple rotation elements. The planetary gear unit is constructed so as to be capable of inputting the reduced speed rotation from the speed reduction planetary gear to the rotation element of the planetary gear unit via a clutch and so forth, and is therefore capable of multiple speed shifting (for example, see Japanese Unexamined Patent Application Publication No. 2001-182785).
In order to construct an automatic transmission that is capable of the above-described multiple speed shifting, providing multiple clutches is necessary in order to change the transmission path that inputs the rotation into the various rotation elements of the planetary gear unit. However, depending on the placement location of these clutches, the various linking members that link these clutches and the various rotation elements of the planetary gear unit, the linking member which requires a large torque may rotate at a high rotation due to the speed shifting (greatly accelerated rotation as to the input rotation). In this instance, the linking member, through which a large torque may be transmitted and also the rotation thereof is a high rotation, requires a high level of rigidity. However, because the linking member is placed on the outer circumferential side, the linking member must be made larger so as to secure the strength of such a linking member. Therefore, not only does this become a hindrance to making the linking member lightweight, but the inertia force according to the increased diameter and increased weight also increases. This prevents improvements to weight saving and controllability in the automatic transmission.
Further, the hydraulic servos of these multiple clutches require an oil line to be provided between the members that rotate relatively, so as to be supplied with hydraulic oil, and sealing rings that seal between these members that rotate relatively need to be provided. However, when a large number of sealing rings are provided, sliding resistance is generated between these members that rotate relatively. There is thus the disadvantage of poorer efficiency of the automatic transmission and reduced controllability thereof.